Large Diamond Crystals Research Articles

Diamond coatings on femtosecond-laser-textured stainless steel 316 surfaces for enhanced adherence

A challenge for directly coating diamond on metallic substrates is the large residual stress near their interfaces due to the large mismatch in the coefficients of thermal expansion (CTEs) that leads to cracking or delamination of the diamond coatings from the substrates. In this work, femtosecond (fs)-laser texturing was applied to fabricate various periodic microgrids on stainless steel (SS) 316 substrates for enhancing the adherence between the SS 316 substrates and the diamond coatings grown using the laser-assisted combustion flame chemical vapor deposition (CVD). Through adjusting the dimensions of the microgrids with different fs scanning parameters, the diamond coatings with a maximum thickness of 19 μm can be grown with quality factors up to 96 % as analyzed by Raman spectroscopy. The corresponding large diamond crystals with an average grain size of 9 μm can be obtained on SS316 substrates by optimizing the fs-laser texturing process. The enhanced adherence between the SS 316 substrates and diamond coatings can be attributed to the stress relief and the improved mechanical bonding. The growth kinetics of the diamond coatings on fs-laser-textured SS 316 substrates were also revealed through the phase constitutions and morphology characteristics. This work is anticipated to provide a new strategy and guidance for the growth of diamond coatings on metallic materials with strong adherence at the interfaces.

Dependence of static strength of large crystals of synthetic diamond type ib of octaedric habitus, after chemical-thermal time and time

Increasing demands on the quality of drilling tools are forcing us to revise the traditional methods of their production and develop new alternative technologies. Some issues related to the possibility of increasing the efficiency of a drilling tool using diamond single crystals are considered. It has been suggested that a further reserve for improving the quality of drill bits lies in the use of large, high-strength, non-magnetic diamonds. Scientific research in this area has shown that the efficiency of the drilling process largely depends on the mechanical properties of single crystals, such as tensile strength and hardness. The grains operate under a load close to critical, which can lead to the complete destruction of single crystals instead of gradual chipping with the formation of new cutting edges. The results of an experimental study of the influence of individual stages of the drilling tool manufacturing process, namely, chemical-thermal treatment and annealing at 1150°C, on the static strength of large type Ib synthetic diamond crystals with an octahedral habit are presented. The dependence of this quantity on the geometric dimensions of single crystals was obtained for the first time. The achieved maximum value of static strength was 8750 N. It was experimentally confirmed that with an increase in the breaking load, the size of the fragments decreases. In order to ensure sufficient strength of the cutting part of the drilling tool, it is advisable to limit the size of single crystals to 1000–1200 µm, since the critical load values ​​for them are higher than for crystals whose size is 1300 µm or more, which, according to the theory, is associated with an increase in the number of defects and inclusions in proportion to size. The performed analysis made it possible to make adjustments to aspects of the manifestation of the scale effect when testing the strength properties of diamond single crystals.

Fourier Transform Limited Linewidth of Optical Transitions in Single SiV Centers in “Adamantane” Nanodiamonds

Silicon-vacancy (SiV) color centers in diamond offer a promising system for quantum information applications owing to their intense narrowband emission and optically detectable spin states. Here, the fluorescent properties of ensembles and single SiV centers in diamonds obtained by high-pressure high-temperature synthesis from adamantane (below referred to as adamantane diamonds) are investigated at liquid-helium temperatures. Ensembles of SiV centers (~103) are studied in large diamond crystals (1–2 µm in size). Despite the large number of excited centers, the fine structure of the zero-phonon line, corresponding to four allowed optical transitions between the ground- and excited-state doublets of the SiV center, can be observed in the fluorescence spectra of these crystals. The width of individual lines is in the range of 60–80 GHz, which is explained by their inhomogeneous broadening. Single SiV centers are studied in diamond crystallites with sizes of about 200 nm. The width of the narrowest transition lines observed in the fluorescence spectra of single SiV centers under resonant excitation is almost three orders of magnitude smaller than linewidths in the spectra of SiV ensembles and is as small as 94 MHz; i.e., these lines are so narrow that their width is determined by the lifetime of the upper state of the transition. Therefore, adamantane nanodiamond features the narrowest emission line width of a single SiV center at cryogenic temperatures among other types of SiV-con-taining nanodiamonds of similar sizes obtained by the high-pressure high-temperature and chemical vapor deposition techniques.

Research on the Restricted Growth of High-Quality Large Cubic Gem Diamond Crystals

In this paper, cubic gem diamond crystal was grown via the temperature gradient under high pressure and high temperature, with self-made alloy solvent and through adjusting the process of assembling and synthesis appropriately. Crystal characters of large hexahedral cubic diamond crystals grown during different times were researched, and the results show that, the radial growth rate of the synthetic crystal is larger than that of the axial growth rate under the experimental conditions. The radial growth rate of the synthesis of the crystal is 3.75 times than that of the axial growth rate within 20 hours. The synthesized high quality diamond crystal has cubic hexahedral morphology and high repeatability, which will be beneficial to the industrialization of high quality cubic hexahedral diamond crystal.

Морфология и структурное состояние частиц нанопорошков, полученных измельчением природного алмаза и методом детонационного синтеза

A complex of high-resolution methods has revealed that the nanopowder particles obtained by milling natural diamonds have a wider variety of sizes and predominantly of lamellar shape in contrast to detonation synthesis nanopowder, which consists mainly of similar-sized and isometric particles. The primary particles of the nanopowder obtained by milling, as well as detonation synthesis nanodiamonds, consist of diamond nuclei with cubic crystal lattices surrounded by shells with complex structures, which are formed from carbon atoms in the sp2-state and impurities. A noticeable increase in interatomic distances in nanodispersed diamond crystals has been established compared with those for large diamond crystals.

Growth characteristics of type IIa large single crystal diamond with Ti/Cu as nitrogen getter in FeNi–C system**Project supported by the Natural Science Foundation of Henan Province of China (Grant No. 182300410279), the Key Science and Technology Research Project of Henan Province of China (Grant No. 182102210311), the Key Scientific Research Project in Colleges and Universities of Henan Province of China

High-quality type IIa large diamond crystals are synthesized with Ti/Cu as nitrogen getter doped in an FeNi–C system at temperature ranging from 1230 °C to 1380 °C and at pressure 5.3–5.9 GPa by temperature gradient method. Different ratios of Ti/Cu are added to the FeNi–C system to investigate the best ratio for high-quality type IIa diamond. Then, the different content of nitrogen getter Ti/Cu (Ti : Cu = 4 : 3) is added to this synthesis system to explore the effect on diamond growth. The macro and micro morphologies of synthesized diamonds with Ti/Cu added, whose nitrogen concentration is determined by Fourier transform infrared (FTIR), are analyzed by optical microscopy (OM) and scanning electron microscopy (SEM), respectively. It is found that the inclusions in the obtained crystals are minimal when the Ti/Cu ratio is 4:3. Furthermore, the temperature interval for diamond growth becomes narrower when using Ti as the nitrogen getter. Moreover, the lower edge of the synthesis temperature of type IIa diamond is 25 °C higher than that of type Ib diamond. With the increase of the content of Ti/Cu (Ti : Cu = 4 : 3), the color of the synthesized crystals changes from yellow and light yellow to colorless. When the Ti/Cu content is 1.7 wt%, the nitrogen concentration of the crystal is less than 1 ppm. The SEM results show that the synthesized crystals are mainly composed by (111) and (100) surfaces, including (311) surface, when the nitrogen getter is added into the synthesis system. At the same time, there are triangular pits and dendritic growth stripes on the crystal surface. This work will contribute to the further research and development of high-quality type IIa diamond.

C3H6N6 doping effect of synthetic diamond under high pressure and high temperature

In this paper, large diamond crystals were successfully synthesized under 5.6 GPa at temperature 1513 and 1553 K with melamine (C3H6N6) additive. Fourier transform infrared spectroscopy (FTIR) indicated C3H6N6 is an ideal nitrogen source for large diamond crystal synthesized by temperature gradient method (TGM), but its hydrogen is not absorbed by diamond. With the increase of C3H6N6 content, the colour of diamond changed from yellow to green, and the highest nitrogen content of diamond is 2300 ppm. High synthesis temperature can effectively reduce the formation of defects and play a key role in the formation of C-centers during diamond growth. Surprisingly, diamond is likely to grow into twin crystal when the C3H6N6 content is 0.1 wt%. In the process of diamond growth, carbon atoms of C3H6N6 are likely to serve as carbon source to form plane dislocations, which eventually lead to the formation of twin diamond. Raman spectra show that there are few crystal defects in diamond synthesized with C3H6N6 as dopant.

Mapping of individual dislocations with dark-field X-ray microscopy

This article presents an X-ray microscopy approach for mapping deeply embedded dislocations in three dimensions using a monochromatic beam with a low divergence. Magnified images are acquired by inserting an X-ray objective lens in the diffracted beam. The strain fields close to the core of dislocations give rise to scattering at angles where weak beam conditions are obtained. Analytical expressions are derived for the image contrast. While the use of the objective implies an integration over two directions in reciprocal space, scanning an aperture in the back focal plane of the microscope allows a reciprocal-space resolution of ΔQ/Q < 5 × 10−5 in all directions, ultimately enabling high-precision mapping of lattice strain and tilt. The approach is demonstrated on three types of samples: a multi-scale study of a large diamond crystal in transmission, magnified section topography on a 140 µm-thick SrTiO3 sample and a reflection study of misfit dislocations in a 120 nm-thick BiFeO3 film epitaxially grown on a thick substrate. With optimal contrast, the half-widths at half-maximum of the dislocation lines are 200 nm.

Synthesis of large diamond crystals with C3H8N4O2 as organic additive under HPHT conditions

Diamond crystals were successfully synthesized in a NiMnCo-C system by adding Malonic acid dihydrazide (C3H8N4O2) as an organic additive. The synthesized conditions in a series of experiments were about at 1300 °C–1400 °C and 6.0 GPa–7.0 GPa. The color, morphology, and inclusions of the synthetic diamond crystals were characterized by optical microscopy, Fourier transform infrared (FTIR) spectroscope and Raman spectroscope, respectively. The color of the synthesized diamonds changes from light yellow to green with increasing amounts of C3H8N4O2. The morphology of the synthesized diamonds exhibited triangular shape with abundant {111} faces. The FTIR spectra indicated that the nitrogen concentration increased whereas the hydrogen and oxygen concentration decreased with increasing concentration of the C3H8N4O2 additive. The Raman peak positions exhibited a systematic downshift with increasing amounts of C3H8N4O2 additive. According to the synthesized resultant, with increased the content of the C3H8N4O2 additive, the quality of synthesized diamond gets worse. It is interesting that the diamond content more nitrogen and less hydrogen and oxygen with increasing the C3H8N4O2 additive. By studying the effects of nitrogen, hydrogen and oxygen coexistence on the synthesis of diamond, it is would to speculate that the natural diamond nucleation and growth environment may be content more nitrogen source and less hydrogen and oxygen.

Shape controlled growth for type Ib large diamond crystals

The shape controlled growth of diamond is beneficial to its subsequent processing. The shape controlled growth for abrasive grade diamond, whose particle size is less than 1 mm, has been studied extensively, while the shape controlled growth of large diamond crystals, which have important commercial and scientific applications, has not been investigated in detail. Therefore, it is necessary to do further researches. In this study, we synthesize large type Ib diamond crystals and investigate their growth shapes at pressures of 5.3-5.9 GPa and temperatures of 1200-1370℃, by using Fe64Ni36 alloy as the catalyst and (100) or (111) face of seed as growth face. Experimental results show that for the diamond crystals grown along the (100) face, the crystal shapes presents plate shape at 1206-1215℃, tower shape at 1216-1260℃, and tower steeple shape at 1261-1360℃; in sequence while for those grown along the (111) face, the crystal shape is of tower at 1233-1238℃ and becomes plate at 1239-1364℃. The ratio of height to diameter, which can provide a standard to quantify the shape of a diamond, is used to describe the crystal shape in detail. For large diamond crystals growing along the (100) face, under a high pressure of 5.6 GPa, the ratio of height to diameter increases with temperature increasing but the ratio of height to diameter, when growing along the (111) face, decreases. The shape distributions of large diamond crystals in the V-shaped region can be determined in the experiments of large diamond crystal synthesis at different temperatures (1200-1370℃) and pressures (5.3 GPa, 5.6 GPa, 5.9 GPa). The lower limit temperature of large diamond crystal growing along the (111) face in the V-shape region is obviously higher than that growing along the (100) face, but the difference between the higher limit temperatures for growing along these two faces is not obvious. The difference between the lower temperature limits of large diamond crystals growing along the (100) and (111) face can be explained by the different energies of the crystal surface and diamond/graphite equilibrium line in the phase diagram of carbon/alloy. Therefore, it has been realized that the shapes for type Ib large diamond crystals are controlled.

Synthesis of large diamond single crystals under high pressure and high temperature through effective utilization of the synthesis cavity

To make maximal use of the synthesis cavity and improve the production efficiency, we designed the double seed bed method to synthesize large diamond crystals under high pressure and high temperature (HPHT) conditions, and the results were both theoretically calculated and verified by experiments.

Study on synthesis and electrical properties of slab shape diamond crystals in FeNiMnCo-C-P system under HPHT

This paper reported the synthesis of slab shape diamond crystals with phosphorus doping from FeNiMnCo-C system in cubic anvil high pressure apparatus (SPD-6×1200) at 5.6GPa and 1250–1320°C. It was attributed to the presence of additive phosphorus that the temperature region of synthetic sheet cubic diamond increases evidently. With the increase of phosphorus content, the surfaces of the slab shape diamond crystals became rough. The results of Raman spectroscopy indicated that the diamonds doped by more phosphorous have more crystal defects and impurities. Furthermore, the electrical properties of the large diamond crystals were tested by a four-point probe and the Hall Effect method. It was shown that the large single crystal samples were n-type semiconductors. This work enriches the application of the slab large diamond crystals.

Effect of B-S co-doping on large diamonds synthesis under high pressure and high temperature

Large single-crystal diamonds with n-type semiconductor were synthesized from S/B-S co-doping FeNiCo-C system under high pressure and high temperature (HPHT) in this paper. It was found that the slight variation of the additive S content had not made obvious change for the color of diamonds synthesized from FeNiCo-C system. The B-S co-doping samples became more transparent and yellow than the samples added alone by S. The analysis of X-ray photoelectron spectroscopy (XPS) spectra and Fourier transform infrared (FTIR) spectroscopy showed the presence of B and S in the obtained diamonds. The electrical properties of large diamond crystals were tested by Van der Pauw method with a four-point probe. The highest value of the hall mobility was 628.726cm2/vs. And the lowest value of the resistivity was 9.33×105Ω·cm with boron additive of 0.8wt.% and sulfur of 2wt.% doping to diamond which was confirmed as n-type. This work indicated that B-S co-doping to synthesize diamond crystals was a trend to promote the electrical properties of large diamond crystals.

Precipitation mechanisms of micro-crystal graphite powder during type IIa large diamonds crystallization process

Type IIa large diamond crystals were synthesized in FeNiCo-C system with Ti (Cu) as nitrogen getter by temperature gradient method (TGM) under high pressure and high temperature (HPHT) conditions. Diamonds grew upon (111) facet under 5.4GPa and 1620K while black powder appeared around the growing diamond crystal. And the black powder covered the growing crystals in cap shape and restrained the diamond growth drastically with growth time prolonged. X-ray diffraction (XRD) and scanning electron microscopy (SEM) were utilized to characterize the black powder described above and the regrown graphite obtained from the growth process of traditional type Ib diamonds. The black powder was proved to be micro-crystal graphite powder and the powder was similar to the regrown graphite. However, there were obvious differences between the micro-crystal graphite powder and the regrown graphite. The present discussion about precipitation mechanisms of micro-crystal graphite powder implied that the added Ti (Cu) and related reaction-products in FeNiCo-C system could change solvent property of the catalyst, which affected solubility curve of graphite. Furthermore, the practice of diamond growth indicated that the relatively high temperature and relatively low pressure conditions were remarkably responsible for the precipitation of micro-crystal graphite powder.

Large single crystal diamond grown in FeNiMnCo–S–C system under high pressure and high temperature conditions**Project supported by the National Natural Science Foundation of China (Grant No. 51172089), the Education Department of Henan Province, China (Grant No. 12A430010), and the Fundamental Research Funds for the Universities of Henan Province, China (Grant No. NSFRF140110).

Large diamonds have successfully been synthesized from FeNiMnCo–S–C system at temperatures of 1255–1393 °C and pressures of 5.3–5.5 GPa. Because of the presence of sulfur additive, the morphology and color of the large diamond crystals change obviously. The content and shape of inclusions change with increasing sulfur additive. It is found that the pressure and temperature conditions required for the synthesis decrease to some extent with the increase of S additive, which results in left down of the V-shape region. The Raman spectra show that the introduction of additive sulfur reduces the quality of the large diamond crystals. The x-ray photoelectron spectroscopy (XPS) spectra show the presence of S in the diamonds. Furthermore, the electrical properties of the large diamond crystals are tested by a four-point probe and the Hall effect method. When sulfur in the cell of diamond is up to 4.0 wt.%, the resistance of the diamond is 9.628×105 Ω·cm. It is shown that the large single crystal samples are n type semiconductors. This work is helpful for the further research and application of sulfur-doped semiconductor large diamond.

Short-pulse excitation of microwave plasma for efficient diamond growth

To realize a variety of potential applications of diamonds, particularly in the area of power electronics, it is indispensable to improve their growth efficiency. Most conventional approaches have tried to achieve this simply by increasing the gas temperature; however, this makes it difficult to grow large diamond crystals. To improve the growth efficiency while lowering the gas temperature, we propose that using a pulse-modulated microwave plasma with a sub-millisecond pulse width can enhance the power efficiency of the growth rate of single-crystal diamonds. We found that using a sub-millisecond pulse-mode discharge could almost double the growth rate obtained using continuous mode discharge for a fixed average microwave power and gas pressure. A comparison between experimental observations of the optical emission spectra of the discharge and a numerical simulation of the gas temperature suggests that a decrease in the gas temperature was achieved, and highlights the importance of electron-dominated reactions for obtaining the enhancement of the growth rate. This result will have a large impact in the area of diamond growth because it enables diamond growth to be more power efficient at reduced temperatures.

High-Pressure Synthesis and Characterization of Ge-Doped Single Crystal Diamond

Here we report on successful synthesis of Ge-doped single crystal diamond at high-pressure high-temperature (HPHT) conditions of 7.0 GPa and 1500–1900 °C from an Mg–Ge–C system. The systematic study of diamond crystallization processes reveals that addition of Ge to the Mg–C system suppresses the intensity of diamond spontaneous nucleation enabling synthesis of relatively large (2–3 mm) diamond crystals via seeded growth. Temperature is found to be a key factor controlling diamond crystallization mechanisms, morphological characteristics, and optical properties of the crystals. It is established that the diamond growth rate depends almost exponentially on the temperature increasing from 3.3 μm/h at 1500 °C to 4.2 mm/h at 1900 °C. Spectroscopic characterization of the synthesized diamonds reveals the abundance of the 2.06 eV Ge–V centers in the photoluminescence spectra confirming successful doping of the diamonds with germanium. The feasibility of the Mg–Ge–C system for growing bulk low-strain diamond dop...

HPHT synthesis and crystalline quality of large high-quality (001) and (111) diamond crystals

High-quality type IIa diamond crystals measuring up to 12mm in diameter (8 to 10 carats) were successfully grown by the temperature gradient method at high pressure and high temperature (HPHT) on defect-free (001)-oriented and (111)-oriented seed crystals. The crystalline quality of the grown crystals was qualitatively evaluated by synchrotron based X-ray topograph and rocking curve (RC) measurements. The results revealed that the crystals grown on (001)-oriented seeds have extremely high quality in the (001) growth sector, which extends straight upward from the seed surface. This sector contains very few dislocations and stacking faults in the upper part in particular, where the RC almost agrees with the theoretical curve. For the crystals grown on (111)-oriented seeds, it was confirmed that crystal defects are fewer in the outer (100), (010), and (001) growth sectors than in the central (111) growth sector extending straight upward from the seed surface. The RCs in selected regions of these {100} growth sectors are close to the theoretical curve, indicating high crystalline quality.

Influence of surface wave plasma deposition conditions on diamond growth regime

The influence of deposition conditions on the diamond thin film growth in linear antenna microwave plasma system, also known as surface wave plasma reactor, is presented in this study. Depending on the process pressure the two growth regimes were identified. At high pressures (over 50Pa) dominates the re-nucleation regime that results in ultra-small diamond crystals, while at low pressures (below 10Pa) dominates the lateral growth regime that leads to formation of large diamond crystals. Next, it was shown that the distance of substrates from “hot” plasma region influences the diamond growth kinetics and results in growth regimes shift. Altogether, the observed results contribute to a better understanding of the diamond growth phenomena in surface wave plasma systems. Thus, it allows controllable growth of diamond films with tailored properties (morphology, roughness, etc.).

Synthesis of a Large Diamond Crystal with a Smooth (100) Facet at its Top Through MPCVD

A large diamond crystal up to 500 μm in diameter with a smooth (100) facet at its top has been synthesized on Mo substrate through microwave plasma chemical vapor deposition (MPCVD). Its morphology and quality were characterized by scanning electron microscopy (SEM), and the growth mechanism was roughly illustrated from both macroscopic and microscopic viewpoints. It was found that morphological instabilities are a major factor resulting in synthesis of large diamond crystals, moreover, high microwave power density (MPD), high CH4 concentrations, high pressure, high substrate surface temperature and the addition of a small amount of O2 were also necessary for the synthesis of large diamond crystals.